Effects of Annealing Temperatures on Microstructure Evolution and Anisotropy of Mechanical Properties of Straightly Rolled Ti-6Al-4 V Alloy Sheet

The Ti-6Al-4 V (TC4) alloy slab is first smelted by industrial electron-beam cold-hearth melting (EBCHM), and straightly rolled, which can greatly reduce the process flow and cost, but the structure and performance depend on the rolling process. Herein, the effects of annealing temperature (943–1093 K) on the microstructure evolution and mechanical properties anisotropy of the direct rolled TC4 sheets are systematically investigated, using x-ray diffraction (XRD), metallographic, SEM analysis, room-temperature tensile, microhardness tests and electron backscattered diffraction measurement analytical methods. The results indicate that, due to the large difference between the rolling reductions in the rolling direction (RD) and Transverse direction (TD) directions, there are certain differences in the microstructures of the cross section and the longitudinal section, while they are all characterized by basket-weave microstructure. The longitudinal and cross-sectional microstructure of the annealed sheet "inherits" the hot-rolled microstructure. The yield strength has obvious anisotropy in RD and TD directions of hot-rolled and annealed sheets, which can be attributed to the differences in microstructure characteristics, texture and substructure. However, a lower annealing temperature cannot effectively eliminate anisotropy. The sheet annealed at 993 K has the least mechanical anisotropy. The results can provide reference for rolling and annealing of TC4 titanium alloy.